The instruments used in cooking foods in a microwave oven are roughly classified into two groups.
Those in one group are free of the influence of microwaves and thus do not heat up themselves. Such cooking instruments include heat-resistant glass containers and containers made of plastic such as polypropylene and polycarbonate. These containers have only the function as vessels or containers.
Those in one other group contain ferroelectric substances such as ferrite (Fe.sub.3 O.sub.4). When the ferroelectric substances are dielectrically heated by microwaves, the foods in the oven are heated by the heat thus produced. Examples of this type are disclosed in Japanese Unexamined Patent Publications 60-223919 and 61-138028.
Of these prior art cooking containers, the latter has a plate in the form of a metal sheet providing a cooking surface and having a ferroelectric material bonded to its back. The dish has its sides bonded to a vessel made of plastic or the like. Thus it was difficult to keep the balance between heat buildup and heat dissipation with such a container.
For the above-described reasons, the prior art cooking containers had the following problems:
I) It is rather difficult to brown the food.
II) If food which is liquid before cooking and solid after cooking and which has a high microwave absorption capacity (e.g. an egg sunny-side up) is cooked in a microwave oven, it might potentially blow up and scatter.
III) If the heat is increased to solve the above problems I and II, the container itself might get broken due to heat storage.
It is an object of the present invention to solve such problems.